The spectral weight of low‐lying excitations in the one‐dimensional spin 1/2 Heisenberg antiferromagnet

We have examined numerical calculations on a spin 1/2 one‐dimensional (1D) Heisenberg antiferromagnet for N=8 spins, both for the states and their spectral weights. This work is of interest because of the recent neutron scattering experiments in CuCl2⋅2NC5D5 which show the spectral weight to be concentrated at the des Cloizeaux and Pearson (dCP) spin wave frequencies. The states form a two‐parameter continuum between the dCp value E1(k) =π‖J‖ ‖sin k‖ and the upper limit E2(k) =2π‖J‖ ‖ sin(k/2) ‖. Though most of the spectral weight is at the dCP frequency for N=8, about 10% of it is found near E2 for k=π. There is no numerical evidence for the existence of singlet bound states as predicted by Ovchinnikov.